Photonic crystal-based lens elements for use in an image sensor

ABSTRACT

The invention, in various exemplary embodiments, incorporates a photonic crystal lens element into an image sensor. The photonic crystal lens element comprises a substrate and a plurality of pillars forming a photonic crystal structure over the substrate. The pillars are spaced apart from each other. Each pillar has a height and a horizontal cross sectional shape. A material with a different dielectric constant than the pillars is provided within the spacing between the pillars. The photonic crystal element can be a lens configured to focus electromagnetic radiation onto an underlying pixel cell.

FIELD OF THE INVENTION

The present invention relates generally to the field of semiconductordevices and more particularly to lens elements utilized in image sensordevices or displays.

BACKGROUND OF THE INVENTION

The semiconductor industry currently uses different types ofsemiconductor-based image sensors that use micro-lenses, such as chargecoupled devices (CCDs), CMOS active pixel sensors (APS), photodiodearrays, charge injection devices and hybrid focal plane arrays, amongothers. These image sensors use micro-lenses to focus electromagneticradiation onto the photo-conversion device, e.g., a photodiode. Also,these image sensors can use filters to select particular wavelengths ofelectromagnetic radiation for sensing by the photo-conversion device.

Micro-lenses of an image sensor help increase optical efficiency andreduce cross talk between pixel cells. FIG. 1A shows a portion of a CMOSimage sensor pixel cell array 100. The array 100 includes pixel cells10, each being formed on a substrate 1. Each pixel cell 10 includes aphoto-conversion device 12, for example, a photodiode. The illustratedarray 100 has micro-lenses 20 that collect and focus light on thephoto-conversion devices 12. The array 100 can also include a lightshield, e.g., a metal layer 7, to block light intended for onephoto-conversion device from reaching other photo-conversion devices ofthe pixel cells 10.

The array 100 can also include a color filter array 30. The color filterarray includes color filters 31 a, 31 b, 31 c, each disposed over apixel cell 10. Each of the filters 31 a, 31 b, 31 c allows onlyparticular wavelengths of light to pass through to a respectivephoto-conversion device. Typically, the color filter array 30 isarranged in a repeating Bayer pattern and includes two green colorfilters 31 a, a red color filter 31 b, and a blue color filter 31 c,arranged as shown in FIG. 1B.

Between the color filter array 30 and the pixel cells 10 is aninterlayer dielectric (ILD) region 3. The ILD region 3 typicallyincludes multiple layers of interlayer dielectrics and conductors thatform connections between devices of the pixel cells 10 and from thepixel cells 10 to circuitry (not shown) peripheral to the array 100.Between the color filter array 30 and the micro-lenses 20 is adielectric layer 5.

Conventional optical lenses, including micro-lenses 20, use curvedsurfaces, either concave or convex, to refract electromagnetic waves toconverge or diverge, but cannot focus light onto an area smaller than asquare wavelength. Micro-lenses 20 are typically made of an oxide with apositive refractive index of around 1.3 to 1.8. Since materials used inthese conventional optical lens elements have a positive refractiveindex, it is necessary that the micro-lenses 20 have curved surfaces tocreate a focal point close to the active area of the photo-conversiondevice 12.

A reduction of the size of the pixel cells 10 allows for a greaterdensity of pixel cells to be arranged in the array 100, desirablyincreasing the resolution of the array 100. Typically, the size of eachmicro-lens 20 is correlated to the size of the pixel cells 10. Thus, asthe pixel cells 10 decrease in size, the size of each micro-lens 20 mustalso decrease. Disadvantageously, however, conventional micro-lenses 20do not scale very well. A reduction in size of micro-lenses 20 islimited by optical and resulting electrical performance. As conventionalmicro-lenses 20 are scaled to smaller sizes approaching the diffractionlimit, the light gathering power, which is an indirect measure ofexternal quantum efficiency, decreases significantly. Accordingly, aspixel cells 10 are scaled, creating micro lenses 20 with desiredproperties, e.g., curvature, focal length, no or minimal loss due todiffraction and interference, among others, is difficult. Therefore, itwould be advantageous to have an improved lens for use in image sensorsto allow better scaling of pixel cells and/or enhanced image sensorperformance.

BRIEF SUMMARY OF THE INVENTION

The invention, in various exemplary embodiments, incorporates a photoniccrystal lens element into an image sensor. The photonic crystal lenselement comprises a substrate and a plurality of pillars forming aphotonic crystal structure over the substrate. The pillars are spacedapart from each other. Each pillar has a height and a horizontal crosssectional shape. A material with a different dielectric constant thanthe pillars is provided within the spacing between the pillars. Thephotonic crystal element can be a lens configured to focuselectromagnetic radiation onto an underlying pixel cell.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages and features of the invention willbecome more apparent from the detailed description of exemplaryembodiments provided below with reference to the accompanying drawingsin which:

FIG. 1A is a cross sectional view of a portion of a conventional imagesensor array;

FIG. 1B is a block diagram of a portion of a conventional color filterarray;

FIG. 2 is a cross sectional view of a portion of an image sensor arrayincluding photonic crystal lenses according to an exemplary embodimentof the invention;

FIGS. 3A-3G illustrates intermediate stages of fabrication of the imagesensor array of FIG. 2 according to an exemplary embodiment of theinvention;

FIGS. 4A-4D are top down views of photonic crystal structures accordingto exemplary embodiments of the invention;

FIG. 5 is a cross sectional view of a portion of an image sensor arrayincluding photonic crystal lenses according to another exemplaryembodiment of the invention;

FIGS. 6A-6B illustrate intermediate stages of fabrication of the imagesensor array of FIG. 5 according to another exemplary embodiment of theinvention;

FIG. 7 is a cross sectional view of a portion of an image sensor arrayincluding photonic crystal lenses according to another exemplaryembodiment of the invention;

FIG. 8 is a cross sectional view of a portion of an image sensor arrayincluding photonic crystal lenses according to another exemplaryembodiment of the invention;

FIG. 9 illustrates an intermediate stage of fabrication of the imagesensor array of FIG. 8 according to another exemplary embodiment of theinvention;

FIG. 10 is a cross sectional view of a portion of an image sensor arrayincluding photonic crystal lenses and a photonic crystal filteraccording to another exemplary embodiment of the invention;

FIG. 11 is a cross sectional view of a portion of an image sensor arrayincluding photonic crystal lens elements according to another exemplaryembodiment of the invention;

FIG. 12 is a cross sectional view of a photonic crystal lens elementaccording to another exemplary embodiment of the invention;

FIG. 13 is a cross sectional view of a portion of an image sensor arrayincluding photonic crystal lens elements, photonic crystal lenses, andphotonic crystal filters according to another exemplary embodiment ofthe invention;

FIG. 14 is a block diagram of an image sensor according to anotherembodiment of the invention; and

FIG. 15 is a block diagram of a processor system including the imagesensor of FIG. 14.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof and illustrate specificembodiments in which the invention may be practiced. In the drawings,like reference numerals describe substantially similar componentsthroughout the several views. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized, and that structural, logical and electrical changes may bemade without departing from the spirit and scope of the presentinvention.

The terms “wafer” and “substrate” are to be understood as includingsilicon, silicon-on-insulator (SOI), or silicon-on-sapphire (SOS)technology, doped and undoped semiconductors, epitaxial layers ofsilicon supported by a base semiconductor foundation, and othersemiconductor structures. Furthermore, when reference is made to a“wafer” or “substrate” in the following description, previous processsteps may have been utilized to form regions or junctions in the basesemiconductor structure or foundation. In addition, the semiconductorneed not be silicon-based, but could be based on silicon-germanium,germanium, or gallium-arsenide.

The term “pixel” or “pixel cell” refers to a picture element unit cellcontaining a photo-conversion device for converting electromagneticradiation to an electrical signal. Typically, the fabrication of allpixel cells in an image sensor will proceed concurrently in a similarfashion.

The term “photonic crystal” refers to a material and/or lattice ofstructures (e.g. an arrangement of pillars) with a periodic alterationin the index of refraction. A “photonic crystal element” is an elementthat comprises a photonic crystal structure.

Embodiments of the invention provide photonic crystal lens elements andan image sensor employing photonic crystal lens elements. Photoniccrystals have recently been recognized for their photonic band gaps. Aphotonic crystal interacts with electromagnetic waves analogously to howa semiconductor crystal interacts with charge particles or their waveforms, i.e., photonic crystal structures are optical analogs ofsemiconductor crystal structures. The fundamental aspect of bothphotonic and semiconductor crystals is their periodicity. In asemiconductor, the periodic crystal structure of atoms in a lattice isone of the primary reasons for its observed properties. For example, theperiodicity of the structure allows quantization of energy (E) levelsand wave vector momentum (k) levels (band structure, E-k relationships).In a similar manner, photonic crystals have structures that allow thetailoring of unique properties for electromagnetic wave propagation.Similar to band gap energy in semiconductors, where carrier energies areforbidden, photonic crystals can provide a photonic band gap forelectromagnetic waves, where the presence of particular wavelengths isforbidden. See Biswas, R, et al., Physical Review B, vol. 61, no. 7, pp.4549-4553 (1999), the entirety of which is incorporated herein byreference.

Unlike semiconductors, photonic crystals are not limited to naturallyoccurring materials and can be synthesized easily. Therefore, photoniccrystals can be made in a wide range of structures to accommodate thewide range of frequencies and wavelengths of electromagnetic radiation.Electromagnetic waves satisfy the simple relationship to the velocity oflight:c=nλwhere c=velocity of light in the medium of interest, n=frequency andλ=wavelength. Radio waves are in the 1 millimeter (mm) range ofwavelengths whereas extreme ultraviolet rays are in the 1 nanometer (nm)range. While band structure engineering in semiconductors is verycomplex, photonic band structure engineering in photonic crystals it isrelatively simple. Photonic crystals can be engineered to have aphotonic band structure that blocks particular wavelengths of lightwhile allowing other wavelengths to pass through.

Photonic crystals can also demonstrate negative refraction. As notedabove, conventional micro-lenses 20 (FIG. 1A) have a positive refractiveindex, and therefore, a curved surface. If, however, a material thatshows a negative refractive index is used, it is possible to refractelectromagnetic waves without the need for a curved surface. This meansa “flat lens” made of a material with a negative refractive index canhave similar properties as a curved lens made of a material with apositive refractive index. See Parimi, Patanjali V. et al., Nature, vol.426, p. 404 (2003), the entirety of which is incorporated herein byreference, for a discussion of experimental results demonstratingnegative refraction at microwave frequencies. See also Pendry, J. B.,Physics Review Letters, vol. 85, no. 18, pp. 3966-3969 (2000), which isincorporated herein by reference.

Conventional silicon dioxide (SiO₂) based micro-lenses 20 (withrefractive index of around 1.5) have a single optical axis and ratherlimited aperture. The lenses 20 cannot focus light into an area smallerthan the square of the wavelength of light that is incident on them. Aflat lens with a negative refractive index is not restricted by aperturesize and can provide effective lenses even as image sensors are scaledto smaller sizes.

Referring to the figures, FIGS. 2, 5, 7, 8, 10, and 11-13 depict aportion of image sensor pixel cell arrays 200A-G, respectively, eachincluding photonic crystal lens elements constructed according toexemplary embodiments of the invention. For illustrative purposes, imagesensor pixel cell arrays 200A-G are CMOS image sensor arrays includingCMOS pixel cells 10. It should be readily understood that embodiments ofthe invention also include CCD and other image sensors.

FIG. 2 depicts a portion of an image sensor pixel cell array 200Aaccording to an exemplary embodiment of the invention. The illustratedarray 200 is partially similar to the array 100 depicted in FIG. 1A. Thearray 200A includes pixel cells 10 having photo-conversion devices 12,ILD region 3, and an optional color filter array 30. Instead ofmicro-lenses 20, however, the array 200A includes photonic crystal lenselements, lenses 220, over the photo-conversion devices 12. Preferably,the lenses 220 have an approximately flat surface. That is, a topsurface 228 and a bottom surface 229 of lenses 220 are approximatelyparallel. The lenses 220 are formed on a lens base 205 as a layer 260,which includes a photonic crystal structure. The photonic crystalstructure of layer 260 can be varied to achieve desired lens 220characteristics such as, e.g., a desired photonic band structure and/ora negative refractive index.

The ILD region 3 can have the exemplary structure shown in FIG. 2. Alayer 271 of tetraethyl orthosilicate (TEOS) is over the substrate 1 andthe devices formed thereon, including the photo-conversion devices 12and, e.g., transistors (not shown) of the pixel cells 10. Over the TEOSlayer 271, there is a layer 272 of borophosphosilicate glass (BPSG)followed by first, second, and third interlayer dielectric layers 273,274, 275, respectively. A passivation layer 276 is over the thirdinterlayer dielectric layer 275. There are also conductive structures,e.g., metal lines, forming connections between devices of the pixelcells 10 and from the pixel cell 10 devices to external devices (notshown).

FIGS. 3A-3G depict process steps for forming the array 200A (FIG. 2). Noparticular order is required for any of the actions described herein,except for those logically requiring the results of prior actions.Accordingly, while the actions below are described as being performed ina general order, the order is exemplary only and can be altered.

Referring to FIG. 3A, the pixel cells 10, including the photo-conversiondevices 12; ILD region 3, including multiple interlayer dielectriclayers, conductive lines (e.g., metal lines), contacts, and connections(not shown), among others; and an optional color filter array 30 arefirst formed by any known method. As shown in FIG. 3A, a lens base layer205 is formed over the color filter array 30. The lens base layer 205can be any suitable material that provides an approximately flat surfaceon which the photonic crystal structure of lenses 220 can be formed. Forexample, lens base layer 205 can be a dielectric layer e.g., a layer ofSiO₂, and can have a thickness within the range of approximately 50Angstroms (Å) to approximately 200 Å.

As shown in FIG. 3B, a layer 261 of material suitable for forming aphotonic crystal is formed over the lens base layer 205. Alternatively,when the array 200A does not include a color filter array 30 and thelens 220 is to be located on the ILD region 3, layer 261 can be formedon an interlayer dielectric layer of e.g., a layer ofborophosphosilicate glass (BPSG), or other interlayer dielectricmaterial.

Examples of materials suitable for forming layer 261 include aluminumoxide (Al₂O₃), tantalum oxide (Ta₂O₃), zirconium oxide (ZrO₂), hafniumoxide (HfO₂), and hafnium-based silicates, among others. It should benoted that certain materials can yield a photonic crystal that absorbs aportion of the photons. If the absorption is excessive, quantumefficiency can be detrimentally affected. Preferably, layer 261 is alayer of Al₂O₃ since it offers less absorption and is similar to SiO₂ inits barrier properties. The thickness of layer 261 can be chosen asneeded or desired. Preferably, layer 261 is formed having a thicknesswithin the range of approximately 100 Å to approximately 5000 Å.

Using a mask level, the Al₂O₃ layer 261 is patterned and etched tocreate a photonic crystal structure of pillars 262, as depicted in FIGS.3C and 3D. Referring to FIG. 3E, the ratio x/d of spacing x between thepillars 262 to the thickness d of layer 261 (or height of the pillars262) can be varied to achieve desired characteristics of the photoniccrystal. Illustratively, x/d is within the range of approximately 1 toapproximately 10. Alternatively, spacer-defined lithography can also beused, particularly if patterning the pillars 262 to achieve a desiredratio x/d is a challenge with existing lithography techniques.

A layer 263 is deposited between the pillars 262 and planarized using aCMP step, as illustrated in FIG. 3F. The layer 263 can be formed of anysuitable material having a low dielectric constant, for example, spun onglass (SOG) or SiO₂, among others. Any suitable technique may be used toform layer 263. For simplicity, the pillars 262 and layer 263 aredepicted collectively as layer 260.

The pillars 262 can be formed having any desired horizontalcross-sectional shape. FIGS. 4A-4C depict exemplary pillar 262 shapes.FIG. 4A is a top plan view of layer 260 with pillars 262 having acircular horizontal cross-sectional shape (i.e., the pillars 262 arecylinders). FIGS. 4B and 4C depict layer 260 including pillars havingrectangular and pentagonal horizontal cross-sectional shapes,respectively.

Also, the pillars 262 can be arranged in a variety of orientations. Asshown in FIG. 4A, the pillars 262 are arranged in columns B in the Ydirection and rows A in the X direction, such that a pillar 262 fromeach consecutive row A forms a column B in the Y direction.Alternatively, as shown in FIG. 4D, the pillars 262 can be arranged inrows along line A in the X direction with each row along line A beingoffset from an adjacent row A, such that pillars 262 from every otherrow A form a column B and B′, respectively, in the Y direction.

Each thickness d, spacing x, x/d ratio, horizontal cross sectional shapeof the pillars 262, orientation of the pillars 262, and the material ofthe pillars 262 and layer 263 are design variables. These designvariables can be chosen to achieve a desired photonic crystal structureand, therefore, the desired properties of layer 260 and the lenses 220.

To achieve the structure shown in FIG. 3G, layer 260 is patterned andetched by known techniques to create the lens 220 directly over thephoto-conversion devices 12. Layer 260 can be patterned to have anyshape. In the exemplary embodiment depicted in FIG. 3G, layer 260 ispatterned and etched to form a lens 220 having approximately the sameshape as the photo-conversion device 12 when viewed from a top downperspective.

FIG. 5 depicts a portion of an image sensor pixel cell array 200Baccording to another exemplary embodiment of the invention. In theexemplary embodiment of FIG. 5, the array 200B includes a light blockingregion 240 between its lenses 220. The light blocking region 240 can bea single continuous region, or multiple discontinuous regions. In eithercase, the region 240 is formed as a portion of the layer 260 and has aphotonic crystal structure. The photonic crystal structure of layer 260in light blocking region 240 is formed such that light, or portions oflight, are prevented from passing through region 240 to respective pixelcells 10, as will be explained in further detail below. In this manner,layer 260 has a first photonic crystal structure for lenses 220 and asecond photonic crystal structure for light blocking region 240. Thelight blocking region 240 can serve in place of, or as a compliment to,the metal layer 7 (FIG. 1A).

According to another exemplary embodiment of the invention array 200Bcan be formed as described above in connection with FIGS. 3A-3F, exceptthat layer 261 is patterned and etched such that any one or more of thedesign variables (e.g., thickness d of layer 261, the spacing x betweenthe pillars 262, the ratio x/d, the horizontal cross sectional shape ofthe pillars 262, and the orientation of the pillars 262) is different inone or more regions of layer 260. That is, the photonic crystalstructure of layer 260 can vary between regions of layer 260, to achievethe structure shown in FIG. 5.

For example, referring to FIGS. 6A and 6B, layer 260 is patterned andetched such that lenses 220 and region 240 have different photoniccrystal structures. Specifically, layer 260 is formed having a photoniccrystal structure to achieve the desired lens 220 properties e.g., anegative refractive index. As in the embodiment of FIG. 2, the lenses220 are formed directly above respective photo-conversion devices 12 andcan be formed in approximately the same shape as respectivephoto-conversion devices 12 from a top down perspective, as illustratedin FIGS. 6A and 6B. FIG. 6B is a top plan view of a portion of the FIG.6A array 200B, wherein the dotted lines show the underlying structuresof the pixel cells 10 and photo-conversion devices 12. The layer 260 inthe light blocking region 240, which is between lenses 220, is formedhaving a photonic crystal structure to prevent light, or a portion oflight, from passing through the region 240.

The flat lenses 220 can also be incorporated in a multilayer lens system222, as shown in FIGS. 7 and 8. FIG. 7 illustrates an array 200C withlenses 220 over respective photo-conversion devices 12 and a lightblocking region 240 between the lenses 220. A second photonic crystallens 220′ is provided over the lenses 220 and region 240. As shown inFIG. 7, lens 220′ can be a continuous approximately flat layer 260′including a photonic crystal structure. The photonic crystal structureof layer 260 can be different than that of layer 260′. Lenses 220 and220′ can be separated by a dielectric layer 265 if desired.

In another exemplary embodiment of the invention, the array 200C havinga lens system 222 including lenses 220 and 220′, as shown in FIG. 7, isformed in the same manner as array 200B of FIG. 5, but with additionalprocessing steps. A dielectric layer 265 (e.g., a layer of SiO₂) isformed over layer 260 by techniques known in the art. The dielectriclayer 265 is illustratively formed having a thickness within the rangeof approximately 50 Å to approximately 200 Å. A second photonic crystallayer 260′ having a photonic crystal structure is formed over thedielectric layer 265. For clarity, elements with a reference numeral anda “′” are same general elements as those with corresponding referencenumerals without the “′” but they can have a different specific chemicalor photonic structure. Accordingly, layer 260′ includes pillars 262 andlayer 263 of low dielectric constant material, and can be formed in asimilar manner to layer 260, as described above in connection with FIGS.3B-3F and 4A-4D, except that layer 260′ is formed over the dielectriclayer 265 and can have a different photonic crystal structure than thephotonic crystal structures of lenses 220 and region 240 of layer 260.

In the exemplary embodiment of FIG. 7, layer 260′ is formed having auniform photonic crystal structure and serves as a continuous lens 220′over the patterned lenses 220. As noted above, the photonic crystalstructure of lens 220′ can be different than the photonic crystalstructure of lenses 220. That is, one or more of the design variables(e.g., the thickness d of layer 261, the spacing x between the pillars262, the ratio x/d, the horizontal cross sectional shape of the pillars262, the orientation of the pillars 262, and the materials of pillars262 and layer 263) of layer 260′ of lens 220′ can be different than thatof layer 260 of lenses 220.

Although the lens system 222 of FIG. 7 is shown including a continuousflat lens 220′, it should be readily understood that layer 260′ caninstead be patterned and etched to form one or more lenses 220′ overlenses 220. Additionally, layer 260′ can be patterned to have multipleregions with different photonic crystal structures, such as, forexample, light blocking regions 240.

FIG. 8 depicts an array 200D with conventional micro-lenses 20underlying the photonic crystal lens 220. The micro-lenses 20 areseparated by a planarized dielectric layer 265, which provides anapproximately flat surface on which the lens 220 is formed.

The array 200D can be formed in a manner similar to array 200A, exceptthat the lens 220 is formed over micro-lenses 20. As depicted in FIG. 9,a dielectric layer 265 (e.g., a layer of SiO₂) is formed over themicro-lenses 20 by techniques known in the art. Dielectric layer 265 isformed having a thickness greater than the thickness of the micro-lenses20, such that dielectric layer 265 provides an approximately flatsurface on which to form the lens 220. A photonic crystal layer 260having a photonic crystal structure is formed over dielectric layer 265forming lens 220 to achieve the structure shown in FIG. 8. Layer 260 canbe formed over dielectric layer 265 as described above in connectionwith FIGS. 3B-3E and 4A-4D and includes pillars 262 and layer 263 of lowdielectric constant material.

The photonic crystal structure of lens 220 can be formed to achieve thedesired lens 220 properties. That is, design variables (thickness d oflayer 261, the spacing x between the pillars 262, the ratio x/d, thehorizontal cross sectional shape of the pillars 262, the orientation ofthe pillars 262, and the materials of the pillars 262 and layer 263within layer 260′ of lens 220′) are chosen to achieve the desiredphotonic crystal structure of lens 220.

Although the lens system 222 of FIG. 8 is shown including a continuousflat lens 220, it should be readily understood that layer 260 caninstead be patterned and etched to form one or more lenses 220 overmicro-lenses 20. Additionally, layer 260 can be patterned to havemultiple regions with different photonic crystal structures, such as,for example, light blocking regions 240.

According to another exemplary embodiment of the invention shown in FIG.10, an array 200E can be formed having both photonic crystal lenses 220and a photonic crystal filter 530 configured in a Bayer pattern asdescribed in U.S. patent application No. [M4065.1022], which isincorporated herein by reference. For this, the processing stepsdescribed above in connection with FIGS. 3A-3G can be performed with theprocessing steps described in U.S. Patent Application No. [M4065.1022].Although the embodiment of FIG. 10 is illustrated as including lenses220 (FIG. 2) and a Bayer patterned filter 530, it should be understoodthat any combination of photonic crystal lenses 220 and/or lens system222 with one or more photonic crystal filters as described in U.S.patent application No. [M4065.1022] can be used.

According to another exemplary embodiment of the invention illustratedin FIG. 11, an array 200F can be formed including a photonic crystallens element 1101 in place of a portion of the ILD region 3 over thephoto-conversion device 12 in one or more pixel cells 10. Accordingly,as shown in FIG. 11, the lens elements 1101 can be below micro lenses 20and an optional color filter array 30. The lens elements 1101 have aphotonic crystal structure that is configured to focus light onto arespective photo-conversion device 12. The lens element 1101 acts as a“light pipe” by directing light onto the photo-conversion device 12.

Preferably, the lens elements 1101 have a horizontal cross-sectionalshape approximately matching that of the respective photo-conversiondevices 12 and are approximately aligned with the respectivephoto-conversion devices 12. By replacing a portion of the ILD region 3with the lens element 1101 in a pixel cell 10, light can be betterdirected to the photo-conversion device 12 and, thereby, quantumefficiency can be increased optical cross-talk between neighboring pixelcells 10 can be reduced.

The lens elements 1101 are a layer 260 having a photonic crystalstructure and can be formed as described above in connection with FIGS.3B-3E and 4A-4D. Accordingly, the lens element 1101 includes pillars 262and layer 263 of low dielectric constant material. The lens element 1101can be formed on the TEOS layer 271. The lens element 1101 can be formedbefore or after the layers 272-275 of the ILD region 3.

The layer 260 of each of the lens elements 1101 can have a photoniccrystal structure different from that of other lens elements 1101.Accordingly, where pixel cells 10 receive different wavelengths oflight, the photonic crystal structure of the layer 260 for a particularlens element 1101 can be configured to direct a specific range ofwavelengths onto the respective photo-conversion device 12. For example,when a Bayer patterned color filter array 30 is used, as in theillustrated embodiment, the lens element 1101 below the color filter 31a can be configured to direct green wavelengths of light onto theunderlying photo-conversion device 12, the lens element 1101 below thecolor filter 31 b can be configured to direct red wavelengths of lightonto the underlying photo-conversion device 12, and the lens element1101 below the color filter 31 c (not shown) can be configured to directblue wavelengths of light onto the underlying photo-conversion device12. Alternatively, when no color filter array 30 is used, the lenselement 1101 can be configured to be selective for particularwavelengths of light and direct only those particular wavelengths to thephoto-conversion device 12, while preventing other wavelengths of lightfrom reaching the photo-conversion device 12. In this manner, the lenselement 1101 can act as both a lens and a filter.

In an alternative embodiment, the lens element 1101 can include morethan one layer 260. As shown in FIG. 12, the lens element 1101 caninclude layers 260, 260′ and 260″. One or more of the layers 260, 260′and 260″ can have a different photonic crystal structure from another ofthe layers 260, 260′ and 260″. The layers 260, 260′ and 260″ areseparated from one another by dielectric layers 1205.

According to another exemplary embodiment of the invention shown in FIG.13, an array 200G can be formed having photonic crystal elements 1101,photonic crystal lenses 220, and a photonic crystal filter 530configured in a Bayer pattern as described in U.S. patent applicationNo. [M4065.1022]. Although the embodiment of FIG. 13 is illustrated asincluding lens elements 1101 (FIG. 11), lenses 220 (FIG. 2) and a Bayerpatterned filter 530, it should be understood that any combination ofphotonic crystal lens elements 1101, photonic crystal lenses 220 and/orlens system 222, and one or more photonic crystal filters as describedin U.S. patent application No. [M4065.1022] can be used. Additionally,conventional filters and/or lenses can be used in connection with or inplace of the photonic crystal-based components.

A typical single chip CMOS image sensor 1400 is illustrated by the blockdiagram of FIG. 14. The image sensor 1400 includes a pixel cell array200A according to an embodiment of the invention. The pixel cells ofarray 200A are arranged in a predetermined number of columns and rows.Alternatively, the image sensor 1400 can include any pixel cell arrayaccording to an embodiment of the invention, such as any of arrays200B-G.

The rows of pixel cells in array 200A are read out one by one.Accordingly, pixel cells in a row of array 200A are all selected forreadout at the same time by a row select line, and each pixel cell in aselected row provides a signal representative of received light to areadout line for its column. In the array 200A, each column also has aselect line, and the pixel cells of each column are selectively read outin response to the column select lines.

The row lines in the array 200A are selectively activated by a rowdriver 1482 in response to row address decoder 1481. The column selectlines are selectively activated by a column driver 1484 in response tocolumn address decoder 1485. The array 200A is operated by the timingand control circuit 1483, which controls address decoders 1481, 1485 forselecting the appropriate row and column lines for pixel signal readout.

The signals on the column readout lines typically include a pixel resetsignal (V_(rst)) and a pixel image signal (V_(sig)) for each pixel cell.Both signals are read into a sample and hold circuit (S/H) 1486 inresponse to the column driver 1484. A differential signal(V_(rst)−V_(sig)) is produced by differential amplifier (AMP) 1487 foreach pixel cell, and each pixel cell's differential signal is amplifiedand digitized by analog-to-digital converter (ADC) 1488. Theanalog-to-digital converter 1488 supplies the digitized pixel signals toan image processor 1489, which performs appropriate image processingbefore providing digital signals defining an image output.

FIG. 15 illustrates a processor-based system 1500 including the imagesensor 1400 of FIG. 14. The processor-based system 1500 is exemplary ofa system having digital circuits that could include image sensordevices. Without being limiting, such a system could include a computersystem, camera system, scanner, machine vision, vehicle navigation,video phone, surveillance system, auto focus system, star trackersystem, motion detection system, image stabilization system, and datacompression system.

The processor-based system 1500, for example a camera system, generallycomprises a central processing unit (CPU) 1595, such as amicroprocessor, that communicates with an input/output (I/O) device 1591over a bus 1593. Image sensor 1400 also communicates with the CPU 995over bus 1593. The processor-based system 1500 also includes randomaccess memory (RAM) 1592, and can include removable memory 1594, such asflash memory, which also communicate with CPU 1595 over the bus 1593.Image sensor 1400 may be combined with a processor, such as a CPU,digital signal processor, or microprocessor, with or without memorystorage on a single integrated circuit or on a different chip than theprocessor.

It is again noted that the above description and drawings are exemplaryand illustrate preferred embodiments that achieve the objects, featuresand advantages of the present invention. It is not intended that thepresent invention be limited to the illustrated embodiments. Anymodification of the present invention which comes within the spirit andscope of the following claims should be considered part of the presentinvention.

1. A processor system comprising: (i) a processor; and (ii) an imagesensor coupled to the processor, the image sensor comprising: asubstrate, an array of pixel cells at a surface of the substrate, eachpixel cell comprising a photo-conversion device, and at least onephotonic crystal lens element over at least one of the pixel cellsconfigured to focus light onto at least one photo-conversion device, thephotonic crystal lens element comprising a plurality of pillars beingspaced apart from each other, and a material within the spacing betweenthe pillars, the material having a dielectric constant that is lowerthan a dielectric constant of the pillars.
 2. The processor system ofclaim 1, wherein the image sensor is a CMOS image sensor.
 3. Theprocessor system of claim 1, wherein the image sensor is a chargecoupled device image sensor.
 4. The processor system of claim 1, whereinthe photonic crystal lens element has a negative index of refraction. 5.The processor system of claim 1, wherein a shape of the photonic crystallens element is approximately the same shape as the photo-conversiondevice and the photonic crystal lens element is approximately alignedwith the photo-conversion device.
 6. The processor system of claim 1,further comprising a micro-lens over at least a portion of the pixelcells.
 7. The processor system of claim 6, wherein the photonic crystallens element is provided over at least one micro-lens.
 8. The processorsystem of claim 1, wherein the array comprises an interlayer dielectricregion and the photonic crystal lens element is on a same horizontalplane as the interlayer dielectric region.
 9. The processor system ofclaim 1, wherein the photonic crystal lens element is within a pixelcell.
 10. The processor system of claim 1, wherein the at least onephotonic crystal lens element is a photonic crystal layer comprising atleast one lens region configured to focus light onto thephoto-conversion device and at least one light blocking regionconfigured to block at least a portion of light from reaching thesubstrate.
 11. The processor system of claim 10, wherein the at leastone lens region has a different photonic crystal structure than aphotonic crystal structure of the at least one light blocking region.12. The processor system of claim 10, wherein a shape of the lens regionis approximately the same shape as the photo-conversion device and thelens region is aligned with the photo-conversion device.
 13. Theprocessor system of claim 1, further comprising a least two photoniccrystal lens elements over at least one of the pixel cells.
 14. Theprocessor system of claim 1, further comprising a photonic crystalfilter over the substrate for selectively permitting electromagneticwavelengths to reach at least one photo-conversion device.
 15. Theprocessor system of claim 1, wherein the processor system is a camerasystem.
 16. A camera system comprising: (i) a camera system processor;and (ii) an image sensor coupled to the camera system processor, theimage sensor comprising: a substrate, an array of pixel cells at asurface of a substrate, each pixel cell comprising a photo-conversiondevice, and at least one lens element having a photonic crystalstructure over at least one of the photo-conversion devices for focusinglight onto the at least one photo-conversion device, the photoniccrystal structure comprising a plurality of pillars being spaced apartfrom each other, and a material within the spacing between the pillars,the material having a dielectric constant that is lower than adielectric constant of the pillars.
 17. The camera system of claim 16,wherein the photonic crystal lens element comprises a plurality ofpillars spaced apart from each other, a material within the spacingbetween the pillars has a dielectric constant that is lower than adielectric constant of the pillars.
 18. A camera system comprising: (i)a camera system processor; and (ii) an image sensor coupled to thecamera system processor, the image sensor comprising: a substrate, anarray of pixel cells at a surface of a substrate, each pixel cellcomprising a photo-conversion device, and at least one lens element overat least one of the photo-conversion devices, the lens elementcomprising a photonic crystal structure configured such that the lenselement has a negative index of refraction, a top surface and a bottomsurface, the top and bottom surfaces being approximately parallel withrespect to each other, the lens element further comprising a pluralityof pillars being spaced apart from each other, and a material within thespacing between the pillars, the material having a dielectric constantthat is lower than a dielectric constant of the pillars.